Electric heater control

My wife has an electric foot heating mat that gets a little too hot to keep her feet on. Can I use a standard electronc dimmer switch to lower the voltage to this 90 watt 120 volt resistive load, thus lowering the temp?

Could you elaborate a little? Why is the 90 watt resistive heating element any different than an incandescent light bulb? Both are resistive loads with 100% power factor right? Is there something in the electronic square wave dimmer that wouldn't function properly?

A Lutron makes a 300 watt plug in lamp dimmer for about $10, it has a cord and plug on it.
No wiring would be needed, therefore no NEC violation.
My question is; will it work.?
I'm sorry, but I don't think putting a folded up towel on an electric heating device sounds very safe.